Necrotizing fasciitis• http://news.blogs.cnn.com/2012/05/11/victim-of-flesh-eating-bacteria-is-showing-fighting-spirit-dad-says

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• Case Study and Class Discussion- 5/23/2012• Download assignment• Be ready to discuss in class your information

gathered from your case study

Chapter 14Bugs that Resist Drugs

See website

• Learning Objectives• Important Terminology• Power point- posted after chapter is

completed• Case Study and Class Discussion #1- Good and

Bad Bacteria, Worth 10 points, 5/23/2012

What happened to Carlos Don, Rebecca Lohsen, Ricky Lannetti?

• Read before next class period• What MRSA?• Is MRSA linked to Necrotizing Fasciitis?

Prokaryotic Cells

Fimbriae

Nucleoid

Ribosomes

Plasma membrane

Cell wall

Capsule

Flagella

Bacterialchromosome

(a) A typical rod-shaped bacterium

(b) A thin section through the bacterium Bacillus coagulans (TEM)

0.5 µm

MRSA

• Methicillin-resistant Staphylococcus aureus (MRSA)

• Infectious bacterium that has become widespread in recent years and that is difficult to treat with most existing antimicrobial durgs– 94,000 people get sick each year, kill about 19,000 – Formerly outbreaks were primarily in hospitals– New high-risk groups: day care workers, prisoners, sexual

orientations, ethnic groups– Young healthy people are now getting sick

A major public health concern

• Robert Daum, a professor of microbiology, states “WE NEED A PLAN OF ATTACK NOW”– Several species of staph bacteria can cause human

disease– Concerns over S. aureus, that has developed

resistance to antibiotic drugs that normally kill them- penicillins and cephalosporins

Staphylococcus aureus• S. aureus is a bacterium that can be passed from person to

person by direct contact or through shared, contaminated items such as towels and bars of soap.

Staphylococcus aureus• Staph bacteria are harmless to most people who carry them.

Between 30% and 40% of the population carries staph on their skin or in their noses.

Staphylococcus aureus

• Some staph bacteria have developed resistance to antibiotic drugs that once effectively killed them.

• About 1% of the population carries drug-resistant strains of staph.– If you carry staph and aren’t sick, you are

“colonized” but not infected. Could have many different types of staph (MRSA)

Staphylococcus aureus

• In otherwise healthy people, staph infection usually causes only minor skin eruptions such as boils or pustules that can resemble spider bits.

•gives out unpleasant smell mainly when pus oozes out.

Staphylococcus aureus

• People with weakened immune systems are at especially high risk of developing severe diseases such as pneumonia, infections of the bloodstream, or infections of surgical wounds caused by staph.– Some disorders: Lupus, AIDS, Diabetes– Elderly and children– http://www.youtube.com/watch?v=XbguONM0vq

o&feature=related

Staphylococcus aureus

• In recent years there have been several cases of healthy people becoming severely ill from MRSA infection

• Most likely because they were infected by an especially deadly strain of drug-resistant staph.

• Healthy person can become more severely ill:– Procedure that weaken the immune system– Break in skin that becomes infected with staph

Staph bacteria

• How do they cause illness?– Multiply on or in human tissues. Secrete toxic substances

that harm human cells – damage organelles, membranes, etc.

– Range of diseases due to different strains – differ in their genetic makeup

– MRSA is a combination of unique strains of bacteria. Some more deadly than others- drug-resistant strains

– Recently more healthy people are becoming ill due to an especially deadly strain of MRSA

– Ricky’s had the flu? Was the flu caused by MRSA??

Antibiotics

• Antibiotics are chemicals that either kill bacteria or slow their growth by interfering with the function of essential bacterial cell structures.– Certain microorganism, such as the fungus

Penicillium, produce compounds that kill bacteria

– 1928, Alexander Fleming isolated penicillium– Many antibiotics are now synthesized

Drug-resistant stains of Staph

• Resistant to class of antibiotic drug called beta-lactams– Penicillin, cephalosporin antibiotics (methicillin)– Very common. Interfere with the bacteria’s ability to

synthesis a cell walls. Water flow in by osmosis? What is osmosis and what caused the water to flow in???

– Non-beta lactam drugs are used as a treatment for MRSA – vacomycin. Not always effective. Did Ricky or Rebecca respond to vacomycin.

• Carlos had pneumonia. What this caused by MRSA?

• 85% of the causes occur in patients who are hospitalized or in people with immune compromised, or health care worker.

Antibiotics

• Antibiotics have been effective in treating most common bacterial infections (staph), but soon after antibiotics were in general use, microorganisms that could survive antibiotics began to emerge.– Drug-resistant bugs– People are treatable but with fewer options– Sometimes nothing works - death

Acquiring resistance

• Bacteria might never grow resistant to drugs if not for random mutations that create new alleles and generate genetic diversity.

• Bacteria can acquire mutations when their DNA replicates during reproduction.– Define mutation– Define alleles– How do these events contribute to diversity?

Acquiring resistance

• Bacteria reproduce asexually by binary fission – a type of asexual reproduction in which one parental cell divides into two.

Acquiring resistance• Unlike sexual

reproduction, in which gametes from two parents fuse, asexual reproduction does not require a partner.

Acquiring resistance

• During binary fission, a single parental cell simply replicates its single chromosome, grows in size, and then splits into two daughter cells, each with a copy of the parental DNA.

• http://www.youtube.com/watch?v=gEwzDydciWc

Acquiring resistance

• Each time DNA is replicated, there is a chance that genetic mutations will occur,– New alleles will then be carried into each daughter

cell. – Because bacteria reproduce much more rapidly (20

minutes) than other organisms, they accumulate mutations at a relatively high rate.

– New population is a few days. Do mutations occurs in sexual producing organisms? Why are we diverse?

Acquiring resistance• A bacterium can also acquire new alleles

through gene swapping, in which bacteria can swap pieces of DNA with other bacteria.

• Remember DNA encodes for what the carries out the functions of the cell?

How populations evolve

• Any organism can undergo genetic changes that gives it new traits

• An entire population of organisms with a new trait can arise when the environment favors that trait- advantageous to organism

• A population is a group of organisms of the same species living together in the same geographic area. (pond water, prairie, etc.)

How populations evolve

• An entire population of organisms with a new trait can arise only when the environment favors that trait – that is, when carrying the specific trait is advantageous to the organisms carrying it.

How populations evolve

• When a population’s environment favors some traits over others, the frequencies of the alleles that code for those traits in the population change over time. – Bacteria populations with and without antibiotics

• This change in the frequency of alleles in the population over time is called evolution.

How populations evolve

• An organism’s ability to survive and reproduce in a particular environment is call that organism’s fitness.

• The greater an organism’s fitness, the more likely that alleles carried by that organism will be passed on to future generations and increase in frequency.

Antibiotic-Resistance trait

• Becomes common trait• Reproductive edge in an environment in

which antibiotic use has been rampant• In some cases, even though they are resistant

to antibiotics they may now reproduce slower.

Patterns of natural selection• Ultimately, interplay between an organism’s

traits and its environment is what determines what traits will predominate in any population.

• Organisms can be fit in one environment and not in another.

• This process of differential survival and reproduction of individuals within a population in response to environmental pressure is known as natural selection.

How populations evolve• When natural selection favors some traits over others, the

population shows adaptation. In other words, specific advantageous traits become more common in a population over time.

How populations evolve

• Note that evolution by natural selection occurs in populations, not individuals.

• Individual organisms do not experience a change in allele frequencies over time.

• Therefore, individual organisms do not evolve.

Natural selection occurs in patterns

• Scientists have defined three major patterns of natural selection.

Natural selection occurs in patterns

• Directional selection occurs when organisms with phenotypes at one end of a spectrum are favored by the environment.

• From populations sensitive to drugs to ones that resist drugs

Natural selection occurs in patterns

• Stabilizing selection occurs when organisms with phenotypes near the middle of the phenotypic range of variation are favored by the environment.

Natural selection occurs in patterns

• Diversifying selection occurs when organisms with phenotypes at both extremes of the phenotypic range of variation are favored by the environment.

MRSA

• Would Carlos, Rebecca, Ricky have survived if we didn’t use so many different antibiotics???

• MRSA first emerged in hospitals in 1960s– Remember new strains may not sicken the patient

but can be passed on others that may become very ill.

– Hand-washing important in hospitals– Strains in community appear different than strains in

the hospital (USA3000 is more virulent than other strains – necrotizing fasciitis)

Stopping superbugs• Because the use of antibiotics can drive bacterial populations

to evolve resistance, antibiotic resistance is inevitable. The best way to control resistance is to change practices that enable resistant strains to thrive.

Superbugs

• Over 200 species of bacteria cause human diseases – Salmonella, Pneumonia, tuberculosis, gonorrhoeae

• Getting harder to treat Salmonella food poisoning- drug-resistance– Humans have contributed to the resistance by

haphazard use and overuse of antibiotics– Agriculture – shrimp in the news????– Vaccines??? Haemophilus influenza - pneumonia